1. Field of the Invention
The present invention relates to an apparatus and a method of registering the location of a portable communication terminal, and a mobile communication network.
2. Description of the Related Art
As is widely known, it is a general practice in the mobile communication service to store the location of each portable communication terminal in a storage unit (a so-called location register) so that an incoming call can be received wherever the portable communication terminal such as a cellular phone is located. More specifically, a mobile communication service area is divided into a plurality of registration areas, and every portable communication terminal is registered in the location register in association with a registration area. Registration of portable communication terminal is conducted periodically and also as a portable communication terminal moves as follows; when a portable communication terminal moves from one registration area to the other, a location registration request specifying the registration area after the movement is transmitted to the network. The registration area of the portable communication terminal stored in a storage unit is updated according to this location registration request.
However, when a train with a lot of passengers possessing portable communication terminals moves from one registration area to the other, lots of location registration requests are transmitted from their portable communication terminals, and a problem occurs in that network traffic increases temporarily and considerably.
To solve the above drawback, for example, Japanese Patent Application Publication No. 11-46380 discloses a mobile communication system in which location registration requests from a plurality of portable communication terminals in a train are represented by one location request by a communication unit installed in the train. In this mobile communication system, a plurality of portable communication terminals located in the train register their locations with the above communication unit as an imaginary base station and, when the train moves from one registration area to the other, the communication unit transmits a location registration request to a control station via a base station. In this way, and location registrations by a plurality of portable communication terminals in the train is represented by a communication unit.
However, in the mobile communication system disclosed in the above Japanese Unexamined Patent Application Publication, communication units in trains must transmit location registration requests to the control station. Hence, a circumstance is still left unchanged in an urban area with considerably many trains in that the control station must receive a large number of location registration requests. Therefore, there is a limit in sufficiently reducing network traffic between base stations and a control station even if the above mobile communication system is used.